I.UEDEKING THE HYDRATION OF COLLOIDS. 377 



light. Clusters of ice crystals had segregated from the mass. Our 

 conclusions are that gelatine solutions do not solidify as a whole 

 when subjected to low temperatures, but become partially disso- 

 ciated. The amount of dissociation is directly proportional to 

 the degree of hydration and the depth of temperature. 



These results differ from those of Guthrie, who did not exam- 

 ine the circumstances in polarized light. Only when examined 

 in this way can the process of freezing of colloid hydrates be 

 understood. 



III. — <'oiiil('iiNa(ioii ill thp i>rores.*« of Hydration. 



As we found that by the process of hydration of colloids heat 

 IS evolved, we should expect it to be attended by condensation. 

 The densities of gelatine solutions of 50, 25 and 10 p. ct. were 

 determined. The densities of solutions of these strengths were 

 also calculated. Following are the results : 



50 per cent. Gel. sp. gr. found, 1.22S sp. gr. calc. i-iSjS Dift". 0.422 

 25 " " " " 1-153 " " 1-0929 " .0601 



10 " " " " 1.064. " " 1. 0165 " -0485 



We see that the calculated spec. grav. is less than the observed 

 spec. grav. in every instance. la other words, water unites with 

 gelatine with condensation. The first equivalents of water are 

 condensed more than the equivalents bound later. In this respect 

 the hydration of colloids is analogous to the hydration of salts. 

 In the 50 p. ct. gelatine solution, condensation of 0.423 is ob- 

 served ; in tlie 25 p. ct. gelatine solution, the condensation is 

 .0200 ; and, final y, in the 10 p. ct. gelatine solution, the conden- 

 sation is .0054. We see that the force of chemical affinity is like 

 the force of gravitation ; it diminishes with the distance. The 

 first equivalents of water are near the center of attraction, the 

 molecule of colloid, and are consequently bound with superior 

 force. 



The above is a mere sketch of the work on which we base the 

 results given. Tiie detail would hardly be of interest. 



It was our purpose to bring certain physical phenomena atten- 

 dant on the process of hydration into harmony with one another. 

 The process of hydration is accompanied with evolution of heat. 



